Our study group (PROBAGE Working Group) have been recently showed that Lactobacillus reuteri DSM 17938 reduced the duration of diarrhea in children with acute infectious diarrhea, and are safe and well-tolerated. In this study the investigators aim to evaluate the potential effect of Lactobacillus reuteri DSM 17938 on the prevention of antibiotic associated diarrhea in children.